1. Field of the Invention
The present invention relates to a dishwasher for domestic use, and more particularly, to a dishwasher for washing tableware with ionized water.
2. Description of the Background Art
FIG. 19 is a cross sectional view showing a main part of a conventional dishwasher.
Dishwasher 100 shown in FIG. 19 includes a front door 29 which can be opened and closed and through which tableware to be washed is taken in and out, a rack 15 for accommodating tableware 16 to be washed, a washing vessel 12 located under rack 15 for storing washing water 48, a rotary washing nozzle 14 protruding at approximately the center of washing vessel 12, a filter 42 for collecting the solid leavings and the like separated from tableware 16 by washing, a plurality of injection openings 49 provided on washing nozzle 14, a heater 40 provided within washing vessel 12 for heating washing water 48, a washing pump 13 for supplying washing water 48 to washing nozzle 14, a drain pump 17 for discharging washing water 48 to a drain pipe 18, a water feed pipe 19 for feeding washing water 48, a water feed valve 47 for controlling the feeding of water from water feed pipe 19, a drying fan 43 for blowing air for drying of washed tableware 16, an air heater 44 for heating air blowing from drying fan 43, a heat exchange duct 30 for discharging the supplied heated air from a main body to the outside thereof and returning water obtained by condensing vapor to washing vessel 12, and a controller 41 having a CPU for controlling the entire dishwasher 100.
The washing operation of dishwasher 100 will now be described briefly.
First, front door 29 is opened, tableware 16 to be washed is put at a prescribed position of rack 15, rack 15 is placed above washing vessel 12, and thereafter, a specific detergent is put in and operation is started. Then, a prescribed amount of washing water 48 is supplied through water feed pipe 19 into washing vessel 12 by "open" operation of water feed valve 47.
Thereafter, washing water 48 pressurized by operation of washing pump 13 is injected together with the detergent from injection openings 49 of rotary washing nozzle 14 to tableware 16, whereby washing is carried out. The washing step is followed by rinsing and drying steps.
In dishwasher 100, when the washing step is started, washing water 48 is contaminated with dirt attached to tableware 16 and the solid leavings are filtered by filter 42 for collecting the leavings, but washing water 48 is contaminated with liquid dirt such as fats and oils, and washing water 48 with fats and oils is again injected to tableware 16 by washing pump 13.
In such a washing method, if dirt contains a large amount of fats and oils, the washing capability of the detergent is degraded and washing water contaminated with fats and oils which are not emulsified nor dispersed is injected, and therefore, fats and oils are reattached to tableware 16, resulting in difficulty in improving the washing performance.
A method of introducing air into washing water and injecting the same as disclosed in Japanese Patent Laying-Open No. 56-68423, a method of soaking tableware in washing water for a while as disclosed in Japanese Patent Publication No. 6-73514 and the like have been proposed as a method of solving this problem.
Furthermore, a washing method of washing tableware with alkaline ionized water and thereafter rinsing with acid ionized water in order to improve the washing performance is disclosed in Japanese Utility Model Laying-Open No. 5-26051 and Japanese Patent Laying-Open No. 6-319673. With such a washing method, however, a sufficient washing effect cannot be obtained when a particularly large amount of fats and oils are attached to tableware.
Furthermore, Japanese Patent Laying-Open No. 6-319673 discloses that alkaline ionized water has pH in the range from 9 to 11 and that acid ionized water in the range from 2 to 4, but tap water in some areas contains a large number of carbonic acid ions and bicarbonic acid ions, and therefore, the above mentioned values of pH cannot be achieved, resulting an inferior washing effect.
Furthermore, a dishwasher disclosed in Japanese Utility Model Laying-Open No. 5-26051 is structured such that either of alkaline ionized water and acid ionized water produced by a water producing device, which is not used for washing, is discarded, resulting in poor water saving capability.
Furthermore, a dishwasher disclosed in Japanese Patent Laying-Open No. 6-319673 is structured such that electrolytic water (ionized water) produced in an electrolytic water (ionized water) produced in an electrolytic cell is supplied to a washing vessel through a switching valve and a pump, so that manufacturing cost is increased by provision of the switching valve and the pump.